Procedures are being developed for the routine culture of epithelial cells from the endometrium of the pig. Cells flushed from the uterine horns during the proliferative phase of the estrous cycle are grown on Medium 199 in which L-valine has been replaced by its D-enantiomer. Using these cultured cells, we plan to study the induction of a number of proteins, including a phosphatase, leucine aminopeptidase and lysozyme, which are secreted into the intact uterus under the influence of progesterone. We believed that one of these proteins, the purple, iron-containing phosphatase is involved in iron-transport to the fetus. Since this protein can be easily identified by immunological procedures and by its unusual enzymatic and physical properties, we shall use this as a model to study the influence of estradiol and progesterone on rates of induced protein biosynthesis and secretion by the cells. We shall also attempt to detect proteins which appear in the cells soon after application of the steroids relative to those which appear after hours or even days. In order to do this we shall employ two-dimensional electrophoresis in polyacrylamide slab gels followed by autoradiography. We shall also analyze the glycosaminoglycans, collagen and other insoluble proteins associated with the substratum after growing the cells in presence of radioactive precursors for several days. We believe that these materials might correspond to substances normally incorporated into the basement membrane. Soluble glycosaminoglycans of the medium will also be investigated since their production is known to be influenced by progesterone in vivo. We shall develop methods for isolation of the upper surface plasma membrane of the cultured cells in order to compare its composition with that of the lateral or basal cell surfaces. Particular attention will be paid to exposed glycoproteins since these might be involved in the receptivity of the surface towards the conceptus. Using electrophoretic techniques, we shall determine whether the composition of this surface begins to change as the cells are administered progesterone for periods up to 3 weeks. Finally attempts will be made to maintain the young embryos on an underlying layer of cultured uterine epithelium. This knowledge should help our understanding of the role of endocrine components in the development of a receptive uterus.